Disease mechanisms in zaspopathy, a prototype myofibrillar myopathy (MFM): During past year, we generated knock-in mice reproducing human MFM-causing mutation (A165V; collaboration with Shyam Sharan, NCI). Phenotypic characterization of these mice is ongoing. We are currently using gene-editing (CRISPR/Cas9) approach to generate knock in A147T and R268C mutations. We have also established cellular assays to examine the role of different ZASP splice isoforms in mechanosensing properties of actin stress fibers to ultimately understand the cellular and molecular basis for F-actin disruption (with Greg Alushin, NHLBI). We are decorating F-actin with purified ZASP to examine ZASP-actin complex with cryo-EM (with Greg Alushin, NHLBI). We have obtained crystals of ZASP proteins and isotope-labeled ZASP proteins for structural studies using x-ray crystallography and NMR spectroscopy (with Paul Winfield, NIAMS). We have expanded our studies of ZASP in skeletal muscle to nervous system. To investigate the cellular and molecular roles of ZASP in the nervous system, antibodies against specific isoforms of ZASP have been validated in immublotting and immunoprecipitation assays using synthesized peptides, as well as protein extracts from human and mouse tissue. Immunoprecipitation is being pursued to identify binding partners for ZASP in brain and spinal cord. Additional antibodies are being generated for other ZASP isoforms in human and mouse. We have successfully visualized the ultrastructural distribution of ZASP in mouse cultured primary (cortical) neurons (with the help of Susan Cheng of the NINDS Laboratory of Neurobiology), showing that 1) ZASP is present in neurons (confirming our previous findings) and 2) ZASP is found in the cytoplasm and in some post-synaptic structures, but not in presynaptic structures (also supporting our previous findings). We are currently investigating the hypothesis that ZASP distribution in neurons (i.e., association with post-synaptic structures) is activity-dependent. Analysis of ZASP splice variants in mouse brain (carried out by the Frederick National Laboratory for Cancer Research) is being completed (with the help of the NINDS Bioinformatics Section) and will inform ongoing work in neuronal cell systems. Lentiviral particles for shRNA-mediated depletion of ZASP in primary neurons have already been manufactured (with assistance from the NCI Protein Expression Laboratory) and are being tested, while particles for the over-expression of ZASP splice variants are currently being designed. These tools will be useful both in our pursuit of binding partners and in the study of cellular and molecular functions for ZASP. We have used gene editing technology (CRISPR-Cas9) to generate an isogenic induced pluripotent stem cell (iPSC) line from patient derived iPSCs, in which a putative neuropathic mutation in ZASP (R268C) was corrected. Reciprocally, we have introduced the same mutation into a control human iPSC line. These isogenic iPCS lines will be used to investigate neuronal findings in human cells. Gene editing technology is currently being used to produce a targeted mutant mouse model for this mutation and mouse embryonic stem cells are currently being screened. We are in the process of producing two neuron-specific conditional knockout mouse models, using the knockout-first system. In these animals, a reporter gene is expressed instead of the endogenous ZASP, and normal ZASP expression is regained following combinatorial Flp- and Cre-mediated recombination. The reporter line is being 1) crossed to Flp- and Cre-expressing mice to produce tissue-specific (neuronal) knockout mice and 2) crossed with each other to produce homozygote (ZASP-null, reporter expressing) pups, from which tissues are being collected and cultured neurons are being grown. These samples will be used to investigate the expression patterns of ZASP in the nervous system and during development, as well as explore the cellular and molecular roles of ZASP in these tissues. Patient studies: We completed MRI analysis of the NIH Duchenne muscular dystrophy (DMD) Imaging study. We have completed one manuscript highlighting IDEAL-CPMG muscle fat fraction (AFF) and muscle water T2 as useful biomarkers of disease activity and treatment efficacy in DMD. Importantly AFF of all examined thigh muscles correlated with clinical outcome measure of six-minute walked distance (Mankodi, 2016). Other manuscripts are highlighting MRI biomarkers of exercise effects in the lower leg muscles and that of diaphragm and chest wall motion as a measure of pulmonary function (under preparation) as well as myocardium and skeletal muscles of the upper extremity in DMD (submitted). We enrolled 23 subjects into the Myotonic Dystrophy Biomarker study (protocol 14-N-0132) and all subjects have completed 3-month follow up evaluations and 16 subjects completed final evaluation at 1 year. We have identified novel gene defects and known gene mutations in several of our patients including the ones in the Neurogenetics clinic by using NextGen exome analysis. Efforts are underway to characterize the biological effects of the novel variants in cell systems and patient tissues.